Among the information essential to control an engine is information output by a coolant temperature sensor. The coolant temperature sensor detects the temperature of engine coolant and outputs corresponding information. An engine electronic control unit (ECU) receives the information from the coolant temperature sensor and uses the information to help control various aspects of the engine such as ignition timing, idling speed, and fuel injection. When the coolant temperature sensor is malfunctioning and cannot output information on the coolant temperture, or outputs imprecise information, the ECU cannot perform normal control of the engine. Therefore, in the event that the coolant temperature sensor is malfunctioning, the ECU sets up a reference value that is used as a new value of the coolant temperature sensor, and controls the engine using this new value.
A conventional method to control the engine when the coolant temperature sensor is malfunctioning will now be described.
Referring to FIG. 1, an engine control apparatus, which has the capability of operating when the coolant temperature sensor is malfunctioning, comprises a vehicle operation sensor 10. The vehicle operation sensor 10 detects and outputs, among other vital information, ignition information and coolant temperature information that vary respectively according to driver manipulation of an ignition key and vehicle operation. The engine control apparatus also comprises an ECU 20 that receives all the information from the vehicle operation sensor 10. Using the information on the coolant temperature, the ECU 20 determines if the coolant temperature sensor is malfunctioning, and when the coolant temperature sensor is determined to be malfunctioning, establishes a predetermined fixed value as information on the coolant temperature sensor and outputs a control signal to control the engine. The engine control apparatus also comprises a drive control apparatus 30 that varies the ignition timing and adjusts both the amount of fuel that is injected into the engine, according to the engine control signal provided from the ECU 20.
The vehicle operation sensor 10 comprises an ATS 11 that detects a temperature of engine intake air and outputs corresponding information; an ignition coil 12 that detects variations in voltage occurring as a result of changes in engine rpm, and outputs engine rpm information; a coolant temperature sensor 13 that detects the temperature of the coolant and outputs corresponding information; an ignition switch sensor 14 that detects on and off states of the ignition switch and outputs corresponding information, the state of the ignition switch being altered according to driver manipulation of the ignition key; and a throttle valve switch 15 that detects throttle valve opening and outputs corresponding information, the throttle valve opening varying according to driver manipulation of an acceleration pedal.
Referring to FIG. 4, when the driver operates the ignition key to an on position such that power is supplied to the ECU 20, the ECU 20 reads the information on the coolant temperature, which varies according to changing vehicle driving states, output from the coolant temperature sensor 13 in step S500. Next, using this information, the ECU 20 determines whether the coolant temperature sensor 13 is outputting information normally (i.e., whether the coolant temperature sensor 13 is operating properly) in step s510.
In the event that the coolant temperature sensor 13 is not outputting information on coolant temperature or is outputting what is determined to be faulty coolant temperature information, the ECU 20 determines that the coolant temperature sensor 13 is malfunctioning. Accordingly, the ECU 20 sets a fixed value (commonly 35.degree. C.) of the coolant temperature as an initial value WT(n) of the coolant temperature in step S511. Subsequently, the ECU 20 compensates for increases in coolant temperature, cranking, start, after-start, and idling, and outputs a predetermined engine control signal to the drive control apparatus 30 according to the compensated values in step s512. Next, the ECU 20 determines whether the ignition switch has been operated to an off position by the driver through detection of the ignition switch sensor 14 in step S513. If it is determined that the ignition switch has been turned off, all of the control operations are terminated.
However, in step s513 above, when it is determine that the ignition switch has not been controlled to off (i.e., maintained in an on state), the ECU 20 returns to step s510 of determining whether the coolant temperature sensor 13 is malfunctioning, and outputs to the drive control apparatus 30 an engine control signal, which is needed when the engine is started or for warm-up and acceleration after the engine is started. Using the engine control signal, the drive control apparatus 30 adjusts the ignition timing, idling, and fuel injection to levels suitable for when the engine is started, after the engine is started, or during acceleration.
On the other hand, if it is determined that the coolant temperature sensor 13 is operating normally such that it is outputting normal information on the coolant temperature (WT), the ECU 20, using the information provided from the coolant temperature sensor 13, compensates for increases in the coolant temperature during cranking, start, after-start, and idling to drive the engine, then outputs an engine control signal to the drive control apparatus 30 in steps s500.about.s590.
As mentioned above, information on the coolant temperature is used for controlling the driving of the engine when the engine is started, after the engine is started, and during acceleration. Therefore, when the coolant temperature sensor 13 normally detects information and outputs the result, no problem in controlling the engine results. However, when the coolant temperature sensor 13 is malfunctioning, many problems in driving the engine result.
One such problem resulting at the time the engine is started will be described.
Information on the coolant temperature provided from the coolant temperature sensor 13 ranges from -30 to about 100.degree. C. The amount of fuel injected into the engine varies depending on the coolant temperature information provided from the coolant temperature sensor 13. In particular, a large amount of fuel (i.e., a rich air/fuel mixture) must be injected into the engine under cold starting conditions to enable easy starting of the engine. However, if the information on coolant temperature is not output or imprecisely output because of a malfunction in the coolant temperature sensor 13, the ECU 20 uses the fixed coolant temperature, which is applied when the coolant temperature sensor 13 is determined to be malfunctioning, to compensate for an increase in start needed for fuel injection when the engine is started. At this Lime, it the engine is being started under cold start conditions and the fixed coolant temperature is set at 80.degree. C. while the actual coolant temperature is below 0.degree. C., an insufficient amount of fuel is injected into the engine, making it impossible to start the engine. Furthermore, even if the engine is started, the idling state of the engine is unstable until the engine is warmed up. On the other hand, if the outside temperature is hot or if the engine is re-started after some driving such that the actual coolant temperate is 80.degree. C., while the fixed coolant temperature is set at -4.degree. C., too much fuel is injected into the engine such that starting the engine is not possible.